Conditioning sewage waste sludges for dewatering

ABSTRACT

Waste sludges are conditioned for dewatering by intermixing with the waste sludge prior to dewatering an admixture of a watersoluble high-molecular weight nonionic polyacrylamide and a water-soluble salt containing ferric ions.

. H50 Sasso et al.

1 Feb. 15, 1972 Appl. No.2

CONDITIONING SEWAGE WASTE SLUDGES FOR DEWATERING Inventors: RonaldAlfred Lo Sasso; Emerson G. Rausch, both of Coraopolis, Pa.

Calgon Corporation, Pittsburgh, Pa.

Aug. 31, 1970 Assignee:

Filed:

us. Cl ..'....210/52, 210/10 rm. Cl ..C02c 3/00 Field of Search ..210/10, 51-54 References Cited UNITED STATES PATENTS 3,171,804 3/1965 Rice....Ql0/54X FOREIGN PATENTS OR APPLICATIONS 607,440 10/1960 Canada...2|0/53 805,526 12/1958 GreatBritain ..21o/52 OTHER PUBLICATIONSBargman, R. D. et aL, Sludge Filtratignand the use of Synthetic OrganicCoagulants at Hyperion, Sewage and rlw l ie w s QL 3Q. Sep .l25 PP;1072-.

1 Primary ExaminerMichael Rogers Attorney-William L. Krayer and HerbertJ. Zeh, Jr.

57 ABSTRACT Waste sludges are conditioned for dewatering' by intermixingwith the waste sludge prior to dewatering an admixture of awater-soluble high-molecular weight nonionic polyacrylamide and awater-soluble salt containing ferric ions.

6 Claims, No Drawings CONDITIONING SEWAGE WASTE SLUDGES FOR DEWATERINGBACKGROUND OF THE INVENTION This invention relates to the treatment ofwaste. More particularly, this invention is directed to a process forconditioning sludges from municipal and industrial wastes to obtain animproved dewatering step.

Sludge is the major byproduct of industrial and domestic water and wastetreating processes. In fact, one of the major problems in a well-runwater pollution controlprogram is the sludge conditioning method used indewatering sludges. The term sludge dewatering process as used in theart and as used herein means any process which reduces the water contentof the sludge fromits usual value of 93 to 99 percent by weight to about90 percent by weight or less. That is, it concentrates the sludge solidsto about percent by weight or greater.

Waste water sludge is basically characterized according to three factorswhich are (l) sludge source, (2) sludge processing, and (3) degree oftreatment. By sludge source is meant whether the sludge is frommunicipal (domestic) waste water or industrial waste water or acombination thereof. The sludge processing characteristic defineswhether the sludge is raw untreated sludge, anaerobic or aerobicdigested sludge, air flotation sludge or digested elutriated sludge. Thedegree of treatment indicates whether the sludge is primary sludge,activated sludge, waste activated sludge, chemically precipitatedsludge, trickling filter humus or a combination of one or more of thesesuch as waste activated sludge combined with primary sludge. It isgenerally accepted that each individual sludge has a differentcharacterization and this sludge character more or less dictates thedewatering process used.

The various mechanical dewatering processes now commonly used in the artand as used herein are gravity filtration, vacuum filtration,centrifugation, flotation, and sedimentation. However, regardless of themechanical process used for dewatering, it has become standard practicein the art to chemicallycondition the sludge prior to dewatering. Thischemical conditioning of the sludge enhances the mechanical dewateringprocess dramatically. The water content of the sludge can be reducedfrom concentrations in the neighborhood of 93 to 99 percent water tothose of about 60 to 90 percent or less by proper chemical conditioningprior to mechanical dewatering.

The most frequently employed chemical for the conditioning of sludge fordewatering is ferric chloride. The ferric chloride may be used alone orin combination with lime and/or other conditioning agents. Other ferricsalts such as ferric sulfate have been widely used alone and incombination with lime. Some ferrous salts, notably ferrous sulfate, havealso found use in the chemical conditioning of sludges.

More recently, high-molecular weight polyelectrolytes have beenextensively used for chemically conditioning sludges. Thepolyelectrolytes have been used alone and in combination with inorganicchemical conditioning agents such as the ferric and ferrous salts, alumand lime. In most of the combination treatments of the prior art, thesludge is first treated with the inorganic conditioning agent followedby the polyelectrolyte. A few applications use the polyelectrolyte firstfollowed by the inorganic conditioning agent. For some examples of theprior art methods, see Priesing et al., U.S. Pat. No. 3,300,407,

which is directed to a chemical conditioning process using an anionicpolyelectrolyte followed by an inorganic conditioning agent. See alsoBlaisdell et al., U.S. Pat No. 3,l42,638 and 3,423,312, which aredirected to the chemical conditioning of sewage sludges. In addition,Lees U.S. Pat. No. 3,472,767 is directed to the conditioning of sewagesludges with a combination of a cationic polyelectrolyte and an acidsalt containing polyvalent metal ions. Finally, see I-Ironas, U.S. Pat.No. 3,066,095.

SUMMARY OF THE INVENTION We have found that the dewatering of wastesludges is greatly enhanced if the sludge is treated prior to dewateringwith an admixture of a water-soluble highmolecular weight nonionicpolyacrylamide and a water-soluble salt containing ferric ions. Thewaste sludge treated according to our invention dewaters better thansludge treated using prior art methods. Chemical conditioning with anadmixture of the polymer and ferric-containing salt yields a sludgewhich dewaters better than a sludge treated with the ferric-containingsalt alone or the polymer alone. It is also better than a sludge treatedwith the polymer followed by the ferric salt or the ferric salt followedby the polymer. We have found that the use of the admixture gives anunexpected synergistic result compared to the other methods of addition.

Our method of conditioning the sludges comprises adding to the sludgeprior to dewatering from 300 to 3,000 ppm. of an admixture of thepolymer/ferric salt. The admixture is comprised of from 0.05 percent byweight to about 5.0 percent by weight of the polymer and the remainderis the ferric-containing salt.

It is a critical step in the method of our invention that the ferricsalt and polymer are physically blended into a liquid ad-- mixturebefore they are added to the sludge. This physical blending may beaccomplished by forming a dry admixture of the two components which isdissolved prior to using to form a solution having the desired amountsof polymer and iron. The physical blend may also be a concentratedaqueous solution of a polymer/ferric salt admixture which is simplydiluted to the desired solution strength before using. One may alsoprepare a solution of the polymer and a solution of the ferric salt andmix these two solutions together in the desired ratio before adding themto the sludge. There are also other ways of preparing and using thephysical blend of the polymer/ferric-containing salt which are apparentto the skilled artisan. The important factor is that the' polymer andferric-containing salt are physically blended into an aqueous solutionin the desired ratio before addition to the sludge.

As mentioned supra, the polymer of our invention is a watersolublehigh-molecular weight nonionic polyacrylamide. To date, however, it isextremely difficult to prepare a high-molecular weight polyacrylamidethat does not contain even a low percentage of carboxylic groups.Therefore, by a nonionic polyacrylamide," we mean to includepolyacrylamides that contain a small amount of carboxylic groups. Weprefer a completely nonionic polyacrylamide but our invention isfunctional with polyacrylamides containing 2 or 3 percent carboxylicgroups. In addition, the polyacrylamide of our invention does not haveto be a homopolymer of acrylamide. The term polyacrylamide as usedherein therefore includes copolymers of acrylamide and up to about 25percent of other nonionic comonomers. Some of the nonionic comonomersare diacetone acrylamide, hydroxy ethyl acrylate, hydroxy ethylmethacrylate, polyethyleneoxide, n-butyl acrylamide and methacrylamide.It is also within the scope of this invention to use polyacrylamidescontaining up to about 5 percent of a cationic comonomer. Some usefulcationic comonomers are the dialkyl diallyl ammonium chlorides andZ-hydroxy 3 methacryloxypropyl trimethyl ammonium chloride. The termnonionic polyacrylamide" includes copolymers of acrylamide and up toabout 5 percent by weight of a cationic comonomer. While higher levelsof cationic comonomers are compatible with the ferric-containing salts,we prefer to use a nonionic polymer. The preferred comonomer isdiacetone acrylamide. In fact, we have found that copolymers containingas much as 50 percent by weight diacetone acrylamide work very well inour invention. We therefore include in the definition of polyacrylamideas used herein polymers containing up to 50 percent by weight diacetoneacrylamide.

There is no limitation on the molecular weight of a polymer which willwork in our invention. A low-molecular weight polymer is effective in sofar as it conditions the sludge to a certain degree. However, ascompared to a high-molecular weight polymer, the low-molecular weightpolymer is ineffective. Generally speaking, the higher the molecularweight the polymer, the more effective it is in our invention.Therefore, by high-molecular weight polymer," we mean a polymer with amolecular weight of one million or greater. We prefer molecular weightsof l to 20 million or higher.

The ferric conditioning agent of our invention is water-solubleferric-containing salt. We have found that any water-soluble salt whichyields ferric ions in solution will work in our invention. Some of theuseful ferric salts are ferric nitrate, ferric :sulfulc, ferricchloride, ferric oxalate, ferric ammonium oxalmc, fcttlc lormnte, ferriclactate, and ferric bromide. However, we have found that ferric chlorideand ferric sulfate are preferred. Among the preferred compounds, ferricchloride is the more preferred.

We have demonstrated that the method of our invention is a veryeffective sludge conditioning process for dewatering. A series ofBuchner Funnel Tests were run on various samples of sludges obtainedfrom different mideastern municipal water treatment plants. The sludgeswere a combination of domestic ing thoroughly. If two or moreconditioning agents are being applied to the sludge, a thorough mixingis done after each addition. The conditioned sludge is poured into thepreviously prepared funnel and a vacuum applied. The time to draw 75.I25, and 150 milliliters of filtrate from the sludge is recorded.

' in addition, the total corrected volume of filtrate (milliliters offiltrate minus milliliters of chemical added) recovered after 2 minutesof vacuum is recorded. After 2 minutes of vacuum, the test is stoppedand the dryness of cake recorded. The following tables illustrate theresults of some Buchner Funnel Tests.

Table l clearly illustrates the unexpected synergistic effects of ourinvention. The use of the admixture in accordance with our inventionconditions the sludge for dewatering better than the use of the polymerfollowed by the ferric chloride or the ferric chloride followed by thepolymer. Table 2 below illustrates the efiectiveness of the use of theadmixture of our invention. Table 3 shows the effectiveness of the useof the ferric chloride followed by the polymer and the polymer followedby the ferric chloride. A comparison of Tables 2 and 3 once again showsthe unexpected greater effectiveness of our invention.

TABLE I Gone. in M1. of percent Percent P.p.n1. filtrate by wt. ofchange in FeCl P.p.m. alter dewatered sludge Ex. Type of treatmentsolution polymer 2 mln. sludge cone.

Admlxture 1,500 22. 5 180 20 1,000 FeCl; firstpolymer last. 1, 500 22. 5118 4. 8 244 Polymer firstFeC1 last. 1, 500 22. 5 133 6. 97 298Admlxture 1, 500 15 179 19 950 FeCla first-polymer last. 1, 500 15 128.4 5. 58 279 Polymer first-Foch last. 1, 500 15 134. 4 6. 1 305 Admixture1, 500 11.25 176 16. 66 833 FeCl: first-polymer last. 1, 500 '11. 25126. 6 5. 43 271 Polymer firstFeCl; last. 1, 500 11,25 129.6 5. 66 283Adrmxture 1, 500 1. 5 192 2, 500 FeCl; first-polymer last. 1, 500 1. 5109. 9 4. 4 222 Polymer first-FeCl; last. 1, 500 1. 5 111. 9 4. 5 227Admixture 1, 750 8.75 187.5 32 1. 00 FeClr firstpolymcr last. 1 750 8.134.2 6.1 305 Polymer first-FeCl last. 1,750 8. 75 141. 2 6. 8 340Admixture 750 4. 375 185. 5 27. 6 1, 380 FeCla first-polymer last. 1,750 4.375 131. 3 5.8 290 18... PolymerfirstFeCl31ast.. 1,750 4. 375141.3 6. 8 340 TABLE 2 Admix ture Total Gone. in composition Time inseconds to obtain filtrate percent v removed by Wt. Comments P.p.m.P.p.m. '75 ml. m1. ml. after .dewatered on sludge Ex. FeCla polymerfiltrate filtrate filtrate 2 mln. sludge cake 19 1,750 26. 25 27 67 94169 13 Moist.

20.. 1, 500 22. 5 18 48 70 183 23. 5 Dry/moist. 21 1, 250 18. 75 25 68100 163 10.8 Wet/moist. 22 1,750 17.5 24 63 87 173 14.8 Moist. 23 1, 50015.0 20 52 73 182 22.2 Dry/moist. 24.. 1,500 11.3 20 55 78 179 19 Moist.25.- 1,750 8. 75 17 42 57 191 44. 4 Dry. 26.. 1,500 7. 5 17 45 02 18936. 4 Dry. 27 2, 10.0 22 57 1 70 183 23. 5 Dry/moist. 28.. 1,750 4.37517 44 60 189 36. 4 Dry. 29.. 1,500 3. 75 20 50 71 187 30.8 Dry. 30.. 2,5. 0 21 53 75 26.7 Dry. 31.. 1,750 1. 75 17 46 64 192 50 Dry. 32.. 2,0002.0 18 48 68 40 Dry. 33. 1,500 1.5 18 45 04 50 Dry. 34...- 1,250 1.25 1641 56 194 66.6 Dry.

TABLE 3 v Concentratlon in M1. of percent by P pm. filtrate weight Ie01; P.p.rn. after2 dewatered 5 Ex. Treatment solution polymer mlnsludge FeClz first. 1,500 22. 5 122 5. 13 P0lymcr1lrst..-. 1,500 22.5137 6.36 l'eGhllrsl. 1 500 15 132 5.9 l'nlymor 1lrut.... 1,500 15 1386.45 Foul: 11ml ,500 11.3 130 5.7

. l'01ynmrllrnt..,. 1,500 11.21 1:13 0.8

101111: llrnt, 1,700 8.7 138, 0.45 l'olymur first... 1,750 8.7 1:15 7.27FeUh llrnt ,750 4. 4 1-15 0. Polymer llret-..- 1, 750 4. 4 145 7. 27F0013 first 1, 500 1.5 113 4. 6 Polymer first.... 1,500 1. 5 115 4.7

TABLE 4v Concentratlon in M1. of percent by P.p.m. filtrate weight FeChP.p.m. alter 2 dewatered Ex. Treatment solution polymer to sludge 47FeCla alone. 1,750 144 7. 1 do 1 0 165 11.4 d 170 13. 3 175 16 173 14. 8172 14. 3 5 173 14.8 .5 145 7.3 .0 175 16 26.25 165 11.4 20 170 13. 322.5 173 14.8 17. 50 167 12.1

The results in Table 4 again illustrate that the admixture method of ourinvention is an improvement over the prior art. Using the admixtureconditioning method the sludge can be effectively dewatered at lowerdosages of chemical conditioning agent.

In the above tables all p.p.m. were parts per million on a weight basisand all concentrations were in weight percents. The polymer was awater-soluble high-molecular weight nonionic homopolymer of acrylamide.The ferric chloride solution was 44.62 percent by weight ferric chlorideand the sludge had an initial concentration of about 2 percent byweight.

We claim:

1. An improved process for dewatering an aqueous waste sludgecomprising:

a. first forming an aqueous blend of a water-soluble, highmolecularweight polymer consisting essentially of nonionic polyacrylamidecontaining not more than about 3 percent carboxyl groups and aninorganic water-soluble salt-containing ferric ions b. thereafterconditioning the waste sludge with the liquid blend; and

c. subjecting the conditioned sludge to a mechanical dewatering step.

2. A process as in claim 1 wherein the blend, exclusive of water,consists essentially of from 0.05 percent to about 5.0 percent by weightof the polymer and the remainder is the water-soluble salt-containingferric ions.

3. A process as in claim 1 wherein the blend is used in con--centrations of from 300 to 3,000 p.p.m. by weight based on the totalweight of the aqueous sludge suspension.

4. A process as in claim 1 wherein the water-soluble saltcontainingferric ions is ferric chloride.

5. A process as in claim 1 wherein the polymer is a homopolymer ofacrylamide.

6. An improved process for dewatering an aqueous waste sludgecomprising:

a. first forming an aqueous blend of water-soluble, highmolecular weightpolymer consisting essentially of nonionic polyacrylamide containing notmore than about 3 percent carboxyl groups and an inorganic water-solublesalt-containing ferric ions where the blend, exclusive of water,consists essentially of from 0.05 percent to about 5.0 percent by weightof the polymer and the remainder the water-soluble saltcontaining ferricions;

b. thereafter conditioning the waste sludge with from 300 to 3,000p.p.m. by weight of the liquid blend; and

c. subjecting the conditioned sludge to a mechanical dewatering step.

UNITED STATES, PATENT OFMGE CERTIFICATE OF CORREUHQN Patent No. 3, 9Dated Fe r y 5.? 1972 Inventor(s) Ronald Alfred Lo Sasso at a].

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 3, line 8, a should be inserted before "water-301w" Columns 3 and4, Table 1; under heading "Percent change in Sludge conco", next to lastnumber in this column "299" should read 290 Column 5, Table 4, line 35,under heading "M1. of filtrate after 2 mine" the 15th number "150"should read 160 Colwnn, line 37, insert a before "water-sol11ble" Signedand aealed this 7th day of November 1372 EDWARD M.FLETCHER,JR., ROBERTGOTTSCHALH Attestlng Officer Commissioner of Patents FORM (10*59)USCOMM-DC 60375-P69 U S GOVERNMENT PRINING OFFlCE 9S9 ("356335

2. A process as in claim 1 wherein the blend, exclusive of water,consists essentially of from 0.05 percent to about 5.0 percent by weightof the polymer and the remainder is the water-soluble salt-containingferric ions.
 3. A process as in claim 1 wherein the blend is used inconcentrations of from 300 to 3,000 p.p.m. by weight based on the totalweight of the aqueous sludge suspension.
 4. A process as in claim 1wherein the water-soluble salt-containing ferric ions is ferricchloride.
 5. A process as in claim 1 wherein the polymer is ahomopolymer of acrylamide.
 6. An improved process for dewatering anaqueous waste sludge comprising: a. first forming an aqueous blend ofwater-soluble, high-molecular weight polymer consisting essentially ofnonionic polyacrylamide containing not more than about 3 percentcarboxyl groups and an inorganic water-soluble salt-containing ferricions where the blend, exclusive of water, consists essentially of from0.05 percent to about 5.0 percent by weight of the polymer and theremainder the water-soluble salt-containing ferric ions; b. thereafterconditioning the waste sludge with from 300 to 3, 000 p.p.m. by weightof the liquid blend; and c. subjecting the conditioned sludge to amechanical dewatering step.